1. Field of the Invention
The present invention relates to an ink jet recording head structure to be mounted on a recording apparatus of ink jet printing system, an ink jet printer, a powder molding method, a method of manufacturing a recording head structure supporting member that employs the former and a powder molding press apparatus
2. Description of the Related Art
Recording apparatuses of ink jet printing system have been used as means for printing characters and images in colors on paper. Recently there are demands for higher density of printing as the resolution of the output images becomes higher.
An ink jet recording head mounted on a recording apparatus of ink jet printing system may utilize the thermal energy generated by a heat generating resistor, deformation of a piezoelectric element, the heat generated by irradiation of electromagnetic radiation or other means for the pressurizing mechanism that ejects ink droplets toward recording paper.
An ink jet recording head structure that employs the thermal energy generated by a heat generating resistor as the pressurizing mechanism, for example, comprises a flow passage member 23 having a plurality of ink chambers 24 and heat generating resistors 25 for pressurizing ink in the respective ink chambers 24, an ink jet recording head 22 constituted from a nozzle plate 29 that has ink discharge holes 28 communicating with the ink chambers 28, and a support member 30 made of ceramics that has ink delivery holes 31 communicating with the ink chambers 24 of the flow passage member 23 and supports the ink jet recording head 22. The Ink delivery hole 31 consists of an elongated hole 32 having an inclined bottom surface 33 that opens on the ink jet recording head side and deepens toward the center and a small-diameter hole 34 that communicates therewith.
In order to print on recording paper by using the ink jet recording head structure 21, a heat generating resistor 25 is caused to generate heat under the condition that ink is supplied through the ink delivery hole 31 into the ink chambers 24. This causes the generation of bubbles in the ink chambers 24 so as to pressurize the ink in the ink chambers 24, so that ink droplets are discharged through the ink discharge holes 28, thereby printing the ink on the recording paper (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 2001-130004).
In the ink jet recording head structure 21 that utilizes the thermal energy generated by the heat generating resistor 25, interruption of bubbles may occur such that part of bubbles generated in the ink chamber 24 by the heat generated by the heat generating resistor 25 are broken, resulting in separated tiny bubbles staying in the ink chamber 24 and/or the ink delivery hole 31. When these tiny bubbles join with tiny bubbles, which are generated as the ink droplets are continuously discharged, or with subsequently generated bubbles so as to form larger bubbles, pressure in the ink chamber 24 changes leading to a change in the quantity of ink droplets discharged from the ink discharge hole 28, thus affecting the resolution of printing.
When the tiny bubbles staying in the ink delivery hole 31 join with other tiny bubbles and turn into larger bubbles staying therein, ink flow in the ink delivery hole 31 and discharge of ink droplets are impeded, resulting in such troubles as considerably uneven printing density, white spots due to ink application failure and lower printing resolution.
Since the ink delivery hole 31 of the support member 30 is generally formed by blasting or grinding process, there are machining chips and dust that have entered the pores and recesses that open on an inclined bottom surface 33 of elongated hole 32. These machining chips and dust cannot be completely removed by cleaning operation. When ink is supplied into the ink delivery hole 31 that has such elongated hole 32, the machining chips and dust that have entered the pores and recesses which open on the inclined bottom surface 33 mix into the ink. This may cause clogging of the ink discharge holes 28, in the case of a recording head structure provided with the ink discharge holes 28 of which diameter is made smaller as the printing resolution is improved.
The support member 30 is made of sintered ceramics. Press molding method has been employed in the powder molding process in order to efficiently produce a large quantity of such sintered ceramics.
Pressing process by means of an ordinary powder molding press apparatus is schematically shown in FIG. 9(a) through (c). First, ceramic material powder P is poured into a recess 38 formed by a die 35 and a lower punch 37, as shown in FIG. 9(a). Then as shown in FIG. 9(b), an upper punch 36 is lowered so as to press the ceramic material powder P thereby to form a ceramic compact. After pressing, the upper punch 36 is lifted while lowering the die 35, so that the ceramic compact S is taken out from the top of the die 35.
When molding a simple plate-shaped compact as described above, substantially uniform pressure can be applied over the entire surface of the ceramic compact. As a result, variation in density is small throughout the inside of the ceramic compact that is produced, and sintered ceramic body having good quality can be mass-produced without crack due to uneven shrinkage in the ceramic compact during the processes of molding and subsequent firing.
In order to produce sintered ceramics having a step, the molds are divided as shown in FIG. 10(a) through (c), and pressures applied to different portions are individually controlled so as to reduce the differences in density among portions of different thickness.
Specifically, ceramic material powder P is poured into a recess 45 formed by a die 41, a stationary punch 43, and a floating punch 44, as shown in FIG. 10(a). At this time, the floating punch 45 is positioned higher than the stationary punch 43 by a distance of the step height of the ceramic compact multiplied by the compression ratio of the ceramic material powder P. Then as shown in FIG. 10(b), an upper punch 42 is lowered so as to press the ceramic material powder P. At this time, the floating punch 44 lowers due to the pressure to the height of the step of the ceramic compact, so that density of the compact becomes equal between the flat portion and the stepped portion. Then as shown in FIG. 10(c), the upper punch 42 is lifted while lowering the die 41 and the floating punch 44, so that the ceramic compact S is taken out from the top of the die 41.
When manufacturing the support member 30 from ceramics having a through hole of different diameters as shown in FIG. 8(a) through (c), first a plate-shaped ceramic compact is made by a powder molding press apparatus as shown in FIG. 9(a) through (c), and then a compact having a groove 22 and a through hole 23 of small diameter communicating with the groove 22 formed by blasting or the like is sintered, or a compact made by injection molding process is sintered.
However, when manufacturing the support member 30 from ceramics as shown in FIG. 8(a) through (c), the method of forming the through hole of different diameters in a plate-shaped ceramic compact formed by the powder molding press apparatus by blasting or the like as shown in FIG. 8(a) through (c) has such problems as shape and dimensions are subject to variations, longer time is taken for processing operation and problem in the product quality, and the method is not suited for mass production.
In the case of forming a ceramic molding having through hole of different diameters by injection molding, on the other hand, although such a complicated shape as described above can be formed accurately relatively easily, it is necessary to use a mold of complicated shape corresponding to the complicated product shape which leads to a high manufacturing cost, and the speed of molding is low. As a result, the injection molding process is inferior to the powder molding press apparatus in terms of applicability to mass production. Moreover, since the material used in the production includes much binder, the injection molded compact takes time for degreasing four to five times longer than that for the ceramic compact formed by the powder molding press apparatus, thus providing lower productivity.
With this background, the inventors of the present application studied the possibility of integral molding of a ceramic compact that constitutes the support member 30 having a through hole of different diameters shown in FIG. 8(a) through (c) by the powder molding press apparatus shown in FIG. 10(a) through (c) which is superior in mass production. However, it was found that, since such a ceramic compact as shown in FIG. 8(a) through (c) has the inclined bottom surface 33 of which thickness changes continuously as shown in section A, it is difficult to maintain uniform density of the compact in the tapered portion of the inclined bottom surface 33 simply by splitting the mold as shown in FIG. 10(a) through (c), and such problems occur as cracks in the molding and deformation due to shrinkage during sintering.